Two different temp readings, now what?

I have a digital coralife thermometer with the submersible probe, which I have used in my Cichlid tank for the last 3-4 years. In addition I purchased a fully submersible which only reads celsius. The difference when I convert Celcius to Farenheit is almost 5 degrees. The probe is about the same depth as the other but is about 8-9 inches away. I guess I need to put them side by side. Kinda scary though!

 

I used to use one of these.
Coralife Digital Thermometer
I actually had 2 of them, they always read 1.5 degrees different from each other. Then I bought a controller with a temp probe. I found the 2 coralife thermometers read 2-4 degrees cooler than actual water temp.

 

I had two of those Coralife thermometers and they read over 10 degrees difference. Neither were correct. Most of their products aren't very good IME. Go get one of those $2 suction cup alcohol thermometers if you want a decent reading. Or some controllers have good thermometers. Really a lot of the digital ones though don't seem to work well unfortunately.

 

I agree, those glass thermometers are the best $2 you can spend. Don't waste your money on a digital one unless it's a temperature probe on a controller (like the Apex or Reefkeeper).

 

Interesting to hear that feedback. I did put the probe sensor wire next to the other all submerged thermometer and there is 4.5 degrees C. difference. Bummer. I thought the glass thermometers were old school and kind of hazardous because of the potential for glass breakage and mercury? I do have a separate temp probe coming from my titanium heater that goes to the plug in thermostat module, and of course that never seemed to be the same as my thermometers. I guess I'll have to check out a cheap glass one , maybe just to confirm where I am actually at.

 

The glass ones use alcohol (with red dye), not mercury. If it breaks, not too much to be worried about. Pretty hard to break though, as I've had my current one (in my 20g) for over 15 years.

 

OK, sounds good. I was thinking of the old glass floater I used to have as a kid. I'll have to get to the store this week.

 

OK, now I am a little baffled. I got a standard hang-on-the-edge glass thermometer. It is 8 degrees cooler. I had been running my previous digital with an active and successful Cichlid tank for the last several years. I remember changing out the battery at least once. The only thing I can figure is the battery is going weak causing a false read? The only thing I am questioning now is that the 79-80 degree water feels cool to me. It's like I need confirmation, AGAIN!